public async Task <IActionResult> GetOrderItems(int orderId)
        {
            var getOrderExpr =
                from orderResult in RestaurantDomainEx.GetOrder(orderId)
                select orderResult;
            var order = await _interpreter.Interpret(getOrderExpr, Unit.Default);

            var getOrderItemsExpr =
                from orderItemsResult in RestaurantDomain.GetOrderItems(order.Order)
                select orderItemsResult;
            var orderItems = await _interpreter.Interpret(getOrderItemsExpr, Unit.Default);

            return(orderItems.Match(
                       found => (IActionResult)Ok(found.OrderItems),
                       notFound => NotFound()));
        }